A. Field of the Invention
The present invention relates generally to the fields of genetics and molecular biology. More particularly, it concerns genetic screening. In specific embodiments, the invention concerns methods for evaluating a nucleotide expansion, contraction or deletion within a target nucleic acid sequence.
B. Description of Related Art
It has been established that the human genome is not a static entity. Repeating units of about 1 to 4 base pairs in length are particularly prone to instability, which leads to greater variability in the genome. This variability can produce polymorphic loci (e.g., microsatellites, short tandem repeats) that are useful as molecular markers in genetic studies. Additionally, particular diseases arise due to genome instability manifested as nucleotide expansions, contractions or deletions. An example of such a disease is the Fragile-X syndrome. In this case, expansion of a repeating motif (CGG)n in the FMR1 gene, residing on the X-chromosome, can give rise to a pleotrophic phenotype resulting in mild to severe mental retardation. Nucleotide expansions also have been associated with Huntington's Disease (HD) and SBMA (Spinobulbar Muscular Atrophies; SCA1 to SCA8). Additional non-limiting examples of diseases associated with repeat expansions are Dentatrubrual-Pallidoluysian Atrophy, Myotonic Dystrophy, Ataxia syndromes (i.e., Friedrich's syndrome) and Androgen Receptor Disfunction. Telomeric repeat lengths may be correlated to senescence (or the lack thereof).
Generally, high resolution electrophoretic methods, including sequencing, are used to quantify the number of repeats present in an expansion region of a gene. Although very accurate, these methods are slow, expensive and cumbersome for general screening. A method suitable for mass screening and preliminary segregation of samples is therefore needed.